Tabulation racks for use in a tabulation operation are well known in the typewriter and related arts. The tabulation mechanisms permit the machine operator to quickly position printing means relative to paper at a predetermined point on the writing line by depressing a "tab" keybutton. Movement is initiated by the keybutton, and the movement usually is terminated in response to the movement carrying a member into contact with a stop located properly on a tabulation rack. This is used in typing columns of figures, indenting paragraphs, and any other operation that requires positioning the printing means to a specific point each time.
In many typewriters the tabulator stop member terminates tabulation by physically blocking and absorbing the momentum of a moving carriage. In other machines, the tabulator stop member merely positions controlling members which stop movement without substantial impact on the tabulator stop member. This invention is designed for use in a tabulation system in which the tabulation stops do not absorb large amounts of kinetic energy.
This invention employs a spring to provide enough frictional drag to hold simply shaped pins or stops in their set and clear position. Prior art is known showing springs in tabulation racks, specifically: German Pat. No. 745,564 issued in 1944 to Heinrich Kleyer AG, and U.S. Pat. Nos. 2,852,120 to Braun et al and 2,312,676 to Schremp. These patents involve shaped surfaces on the stops to provide positive detenting action. Simple frictional drag is not an essential or inherent part of the functions disclosed.
Accordingly, the three foregoing patents are believed to be of little real significance to the patentability of this invention. No prior art is known in which a tabulation rack or the like employs simple pins having straight surfaces with the pins held at different settings by friction from contact of the straight surfaces with a receiving hole, with sufficient frictional drag created by force from a biased spring or resilient member. U.S. Pat. No. 3,333,669 to Schaefer does employ such friction positioning in a tabulation rack, but the drag force is created by the resilience of the stop members, which are twisted.